﻿using System;
using System.Security.Cryptography;
using System.IO;
using System.Text;

namespace Peer.Security
{
    ///
    /// Security 的摘要说明。
    /// Security类实现.NET框架下的加密和解密。
    ///
    public static class PeerSecurity
    {
        private static string _key = "&a~+1%{#"; 
        ///
        /// 加密URL传输的字符串
        ///
        public static string EncryptString(string str)
        {
            return Encrypt(str, _key);
        }

        ///
        /// 解密URL传输的字符串
        ///
        public static string DecryptString(string str)
        {
            return Decrypt(str, _key);
        }

        ///
        /// DEC 加密过程
        ///
        private static string Encrypt(string pToEncrypt, string sKey)
        {
            DESCryptoServiceProvider des = new DESCryptoServiceProvider();　//把字符串放到byte数组中
            byte[] inputByteArray = Encoding.Default.GetBytes(pToEncrypt);
            des.Key = ASCIIEncoding.ASCII.GetBytes(sKey);　//建立加密对象的密钥和偏移量
            des.IV = ASCIIEncoding.ASCII.GetBytes(sKey);　 //原文使用ASCIIEncoding.ASCII方法的GetBytes方法
            MemoryStream ms = new MemoryStream();　　 //使得输入密码必须输入英文文本
            CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(), CryptoStreamMode.Write);

            cs.Write(inputByteArray, 0, inputByteArray.Length);
            cs.FlushFinalBlock();

            StringBuilder ret = new StringBuilder();
            foreach (byte b in ms.ToArray())
            {
                ret.AppendFormat("{0:X2}", b);
            }
            ret.ToString();
            return ret.ToString();
        }

        ///
        /// DEC 解密过程
        ///
        private static string Decrypt(string pToDecrypt, string sKey)
        {
            DESCryptoServiceProvider des = new DESCryptoServiceProvider();

            byte[] inputByteArray = new byte[pToDecrypt.Length / 2];
            for (int x = 0; x < pToDecrypt.Length / 2; x++)
            {
                int i = (Convert.ToInt32(pToDecrypt.Substring(x * 2, 2), 16));
                inputByteArray[x] = (byte)i;
            }

            des.Key = ASCIIEncoding.ASCII.GetBytes(sKey);　//建立加密对象的密钥和偏移量，此值重要，不能修改
            des.IV = ASCIIEncoding.ASCII.GetBytes(sKey);
            MemoryStream ms = new MemoryStream();
            CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(), CryptoStreamMode.Write);

            cs.Write(inputByteArray, 0, inputByteArray.Length);
            cs.FlushFinalBlock();

            StringBuilder ret = new StringBuilder();　//建立StringBuild对象，CreateDecrypt使用的是流对象，必须把解密后的文本变成流对象

            return System.Text.Encoding.Default.GetString(ms.ToArray());
        }
    }
}
